1. Field of the Invention
The present invention relates to the alkylation of hydrocarbons, and in particular to liquid phase alkylation of aliphatic hydrocarbons in the presence of a supported liquid acid catalyst.
2. Description of the Prior Art
Acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well known process for the preparation of high octane gasoline products. In the past, alkylation of hydrocarbons has been accomplished in liquid phase by mixing paraffins and olefins in the presence of a strong acid catalyst and stirring the mixture until the alkylation reaction was completed. Such a batch process layout requires large reaction volumes and thorough mixing of the alkylation mixture by mechanical mixing means in order to provide intimate contact between the acid catalyst, the reacting hydrocarbons, and the olefinic alkylating agent.
Although being very efficient, a major drawback of the known acid catalysts are their environmental and health risk, when used in large amounts such as in the known batch processes.
An alkylation process using minor amounts of liquid hydrofluoric acid or sulfuric acid is disclosed in U.S. Pat. No. 4,783,567. By the disclosed process, a reaction mixture of an olefinic alkylating agent and a hydrocarbon substrate is contacted with liquid hydrofluoric acid or sulfuric acid in a fixed bed reaction zone comprising particulate contact material. In the reaction zone an emulsion is formed, which is sustained by agitation or turbulence for a length of time, after which it is passed to a settling zone, where separated liquid acid and hydrocarbon phases are formed and withdrawn. The resulting alkylation product has a high octane number, which increases with increasing reactor packing volume.
A disadvantage of the disclosed process, however, is the use of hydrofluoric acid or sulfuric acid alkylation catalysts. Besides being hazardous materials as mentioned hereinbefore, sulfuric acid and hydrofluoric acid are rather unstable or aggressive compound under the reaction conditions used in the alkylation process. At ambient conditions, hydrofluoric acid is a volatile gas, which necessitates the alkylation process to be carried out at low temperatures or at elevated pressure. While sulfuric acid is a liquid with a high boiling point and much easier to contain in the event of an accident, it is consumed in considerable amounts during the process by reduction to volatile sulfur dioxide and other unwanted products.